Han-Ki Kim

Effect of hydrogen peroxide treatment on the characteristics of Pt Schottky contact on n-type ZnO

We report on the formation of good Pt Schottky contacts on the Zn-terminated n-type ZnO (0001) surfaces (∼2×1017cm−3) using surface treatment with a hydrogen peroxide solution. The Pt contacts on organic solvent-cleaned ZnO (0001) show leaky behavior with a high leakage current of ∼−0.05A under −5V reverse bias voltage, whereas the hydrogen peroxide-treated contacts show Schottky behavior with very low leakage current of ∼−6.5×10−8A under −5V reverse bias voltage. Schottky barrier heights estimated from current-voltage and capacitance-voltage characteristics are 0.89 and 0.93eV, respectively. Room-temperature photoluminescence results show that the hydrogen peroxide treatment is fairly effective in removing deep-level defects near the ZnO surface region. In addition, the preliminary deep-level transient spectroscopy result is also presented.

Plasma damage-free sputtering of indium tin oxide cathode layers for top-emitting organic light-emitting diodes

We report on plasma damage-free sputtering of an indium tin oxide (ITO) cathode layer, which was grown by a mirror shape target sputtering (MSTS) technique, for use in top-emitting organic light-emitting diodes (TOLEDs). It is shown that OLEDs with ITO cathodes deposited by MSTS show much lower leakage current (9.2×10−5mA∕cm2) at reverse bias of −6V as compared to that (1×10−1–10−2mA∕cm2 at −6V) of OLEDs with ITO cathodes grown by conventional dc magnetron sputtering. Based on high-resolution electron microcopy, x-ray diffraction, and scanning electron microscopy results, we describe a possible mechanism by which plasma damage-free ITO films are grown and their application for TOLEDs.

Electrical characteristics of Pt Schottky contacts on sulfide-treated n-type ZnO

We have investigated the effect of sulfide treatment on the electrical characteristics of Pt contacts on (000-1) n-type ZnO(∼5×1015cm−3) single crystals. The Pt contact on conventionally cleaned ZnO surface shows an ohmic behavior. However, the contact produces a Schottky behavior, when the ZnO surface is etched in a boiling (NH4)2Sx solution. Measurements show that the Schottky barrier height, ideality factor, and leakage current at −5V of the Pt contact on the sulfide-treated ZnO are 0.79eV, 1.51, and 3.75×10−10A, respectively. Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) examinations indicate the formation of ZnS phase at the Pt∕ZnO interface. Based on the capacitance–voltage, AES, and XPS results, a possible mechanism for the formation of good Schottky contacts is given.

Study of the Electrical and Structural Characteristics of Al/Pt Ohmic Contacts on n-Type ZnO Epitaxial Layer

We have investigated Al/Pt (20/50 nm) ohmic contacts on a n-type zinc oxide (ZnO:Al) epitaxial layer The samples were annealed at temperatures of 300°C and 600°C for 1 min in nitrogen ambient. Current-voltage measurements indicated that the as-deposited sample was ohmic with a specific contact resistivity of 1.25 (±0.05) × 10 -5 Ω cm 2 . However, the annealing at 300°C resulted in a significantly better ohmic behavior, with a contact resistivity of 2 (±0.25) X 10 -6 Ω cm 2 . A further increase in the annealing temperature to 600°C led to a decrease in specific contact resistivity due to extensive interfacial reactions between Al and ZnO. Both Auger electron spectroscopy and glancing angle X-ray diffraction were employed to investigate the nature of the interfacial reaction between the Al/Pt and ZnO layer with increasing annealing temperature. Possible explanation is given to describe the temperature dependence of the specific contact resistivity.

Low-resistance Pt'Pd'Au ohmic contacts to p-type AlGaN

We report on a Pt/Pd/Au metallization scheme for producing low-resistance ohmic contacts to moderately doped p-AlGaN:Mg (1.5×1017 cm−3). Annealed Pt/Pd/Au contact exhibits linear current–voltage characteristics, showing that a high-quality ohmic contact is formed. The Pt/Pd/Au contact exhibits a specific contact resistivity of 3.1×10−4 Ω cm2 when annealed at 600 °C for 1 min in a flowing N2 atmosphere. Using Auger electron spectroscopy and x-ray photoelectron spectroscopy, a preliminary explanation for ohmic contact formation is described.

Interfacial reaction effect on the ohmic properties of a Pt/Pd/Au contact on p-type GaN

We have investigated the effect of interfacial reactions between a Pt(7 nm)/Pd(7 nm)/Au(15 nm) layer and p-GaN on its ohmic contact properties by using Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), and glancing angle x-ray diffraction. The annealed Pt/Pd/Au contact exhibits linear current-voltage characteristics, which indicates that a high-quality ohmic contact is formed. The Pt/Pd/Au contact shows a specific contact resistivity of 3.1×10−5 Ω cm2 when annealed at 600 °C for 2 min in flowing N2 atmosphere. Both AES and XPS results show that the diffusion of Pt and Pd into the GaN surface region results in the formation of gallide and plays an important role in forming a low resistance ohmic contact by the creation of a highly doped p+-GaN surface region.

Power control management for home appliance system

In this paper, a high efficiency and low distortion switching power amplifier is proposed. When the proposed method is applied to existing Home Theater System1, the switching amplifiers efficiency is improved 3 times more than before with 1W audio output and the power reduction is achieved up to 33% with 1W audio output. The proposed power control management achieves high efficiency without audio quality degradation.